The invention relates to a current measuring device having a current carrying conductor in an insulating housing and a Hall sensor arranged in the vicinity of the conductor. Such a current measuring device is described in EP 0 538 658 A1, for example.
Hall sensors can be used to measure the current flowing in a conductor without making contact, as is known. To concentrate the magnetic field of the current, which is responsible for the Hall effect, and to exclude interfering influences, it is general practice to use ferromagnetic elements having a clearance which contains the Hall sensor.
In the current measuring device which is described in the aforementioned document EP 0 538 658 and can be used in power switches and motor protective circuit breakers, the current flows through a coil which is split into two halves and whose common coil former is provided with a pocket for holding the integrated Hall circuit.
DE-A-34 28 392 discloses a similar current measuring device in which a current carrying conductor in the form of a coil or a bent rail surrounds a Hall sensor and is itself surrounded by a ferromagnetic core to concentrate the magnetic field.
Such embodiments of the current measuring device with coils and ferromagnetic cores and the like have the disadvantage that the coils and cores make the structure very large and heavy.
DE-A-195 49 181 discloses a current measuring device in which a Hall sensor is inserted between the limbs of a U-shaped conductor loop, without a ferromagnetic core being connected in between. This measuring device has no shield, however, and is therefore relatively inaccurate and is not suitable for measuring heavy currents, at least.
The invention is based on the object of refining the current measuring device such that it is of simple design, is small and lightweight and can thus be used universally.
The invention achieves this object with the features specified in patent claim 1. Advantageous refinements of the current measuring device according to the invention are specified in the subclaims.
Dispensing with a coil and a ferromagnetic core or another ferromagnetic element not only simplifies the design of the current measuring device, but also means that significantly less heat is produced during operation on account of the fact that transfer losses no longer occur. This is of considerable importance particularly for use in switchboxes.
The two current paths, carrying flow in opposite directions parallel to one another, in the U-shaped conductor loop comprising flat busbars cause the magnetic field, and hence the signal from the Hall sensor, to be virtually doubled.
The current measuring device according to the invention for measuring current without making contact is so small that it can easily be incorporated in measuring boxes and switching devices. The current measuring device according to the invention already integrates the electronics for amplifying and evaluating the measured signal, a temperature compensation means and possibly a control logic unit and a digital display.
The fully closed, insulating cover between the housing with the current carrying conductor and the circuit board with the Hall sensors and the evaluation electronics ensures complete DC isolation of the high-voltage region from the electronic components.
The optionally provided metallic shield around the U-shaped conductor loop reduces the influence of interfering magnetic fields on the Hall sensor.